Railway signaling system



C. F. SCOTT. RAILWAY S'IGNAUNG SYSTEM. APPLICATION FILED DEC. 29, I9l5.-RENEWED JUNE 9,1920.

Patented Nov. 15, 1921.

3d INVENTOR /e: f' Swfi' WITNESSES ATTORNEY UNITED STATES PAJENT OFFICE.

.CHARLES F. SCOT'I'QOF NEW HAVEN, CONNECTICUT, ASSIGNOR TO WESTINGHOUSEELECTRIC AND MANUFACTURING COMPANY A CORPORATION OF PENNSYLVANIA.

RAILWAY SIGNALING SYSTEM.

Specification of Letters Patent.

Patented Nov. 15, 1921.

Application filed December 29, 1915, Serial No. 69,175. Renewed .Tune 9,1920. Serial No. 387,801.

ductors and means for minimizing the inductive disturbances that may beimposed on adjacent electrical circuits by reason of the power currentsflowing in the railway systems. t i In alternating-current railwaysystems, it is usual to insert insulating joints at suitable points inthe rails in order to provide insulated block-sections for the signalingsystems. Each of these block-sections constitutes a section of the trackthat is protected by an indicating device which may be a semaphore orany other convenient signaling means. The operation of this signalingdevice is usually effected by means of a relay excited by signalingcurrents that are confined to the separate block-sections and arederived from a source of power independent of that furnishing thepropulsion currents.

In order that the propulsion currents may flow over the tracks of amulti-track railway system, impedance bonds are usually inserted on'eachside of the insulating joints defining the block sections of each traclcand are connected between the track-sections and tracks in such mannerthat the propulsion currents will normally divide themselves be tweenthe rails of the several tracks.

Adjacent impedance bonds are intercom nected by means of taps disposedat the mldpoints of their windings so that the propuL sion current fromone rail traverses one-half of each winding in one direction, and thecurrent from the other rail traverses the other half of, the. winding inthe opposite direction. Since the currents in the two halves ofthewindings neutralize each other in their magnetizing action on the coremembers of the impedance bonds, the propulsion currents are afforded apath of low rl ilb pedance for their flow along the track. lhe

several tracks are connected to one another the signaling relay which,in turn, controls the operation of the signaling device to indicate theconditions obtaining upon a particular block-section of the railwaysystem.

In alternating-current railway systems, it is desirable to provide meansfor minimizing the inductive disturbances that may arise from the flowof the propulsion currents therein. A very effective means foraccomplishing this object contemplates the inser tion of a number ofseries transformers at spaced intervals in a railway system, the primarywindings of the transformers being connected in series-circuitrelationship with thetrolley or third-rail conductor, and the secondarywindings thereof being connected through impedance bonds to the trackrails and in shunt to the aforementioned insulating joints positioned inthe rails. By confiningthe return flow of the trolley current to thetrack the inductive effects arising from the current flow over thetrolley conductor are substantially neutralized. This system forminimizing inductive interferences is fully described in my co-pendingpatent application, Serial No. 170, filed January 2, 191.5, and whichmatured into Patent No. 1196,5300, Aug. 29, 1916. By inductivelyinterlinking the track and the trolley conductor, as mentioned above,electromotive forces are impressed at intervals in the track whichcompensate for the m1- pedance of the track and serve to confine theflow of the propulsion currents to the track in preference to the earth.If it is desired to interconnect the tracks of a multi-track railroadsystem at points near the middle of the block-sections, it will benecessary to confine the alternating currents adapted to op crate thesignaling apparatus to the separate block-sections in order to affordthe proper protection to the traffic accommodated by the railroad.Therefore, in conjunct1on with the above-mentioned means for minimizingpropulsion currents.

the inductive interferences, I also provide means for permitting thesignaling currents to flow substantially unimpeded in each of theblock-sections of the several tracks, at the same time, insuring thatthe signaling currents of the separate block sections be maintainedindependent of one another.

, An object of my invention is to provide means, in a multi-trackrailway system in which the block-sections of the separate tracks arenot correspondingly positioned,

for dividing each track circuit into a plurality of block sections forsignalmg purposes without breaking the electrical conof the trolleycurrents to the tracks so as to minimize the inductive disturbances thatmay beimpressed upon any adjacent electrical circuit, such as anintelligence-transmission circuit.

F or a better understanding of the nature and scope of my invention,reference may be had to. the following description and the accompanyingdrawing in which the single figure is a diagrammatic representation of arailway system embodying a form of my invention.

Referring to the drawing, a source of alternating current (not shown)supplies propulsion currents to trolley conductors 1 and 2 and to theirassociated tracks 3 and 1, respectively, the latter, in combination,constituting a path for the return flow of the Spaced insulating joints5 are inserted at intervals in the trolley conductor 1, andcorrespondingly positioned insulating joints (S' are inserted in thetrolley conductor 2. His presumed that the block sections comprising theinsulated track-sections are not correspondingly placed in the tracks 3and at, and, for convenlence, I

. assume, in this instance, that the ends of the block sections of thetrack 3 are substantiallypositioued at the mid-points of the blocksections of the track 1. Insulating joints 7 are inserted in each of therails of the track 3 at spaced intervals to define the block sectionsthereof, and other insulating joints 7 of the track 4 are arranged instaggered relationship to the insulating joints 7 of the track 3 todefine the block sections of the track 1. Insulating joints 8 areinserted in each of the rails of the track 3 at points corresponding tothe location of the insulating joints 7 of the track 4: and, similarly,insulating joints 8 of the track 4: are inserted at points correspondingto the location of the insulating joints 7 of the track I). It isapparent, therefore. that the block sections of the tracks 3 and 4 aredisposed in staggered relationship with respect to one another. Ipropose, however, to interconnect the tracks to each other both at theends and the mid points of the block sections aiuh at the same time, toinductively intcrlink the trolley conductors and the tracks to eachother in order that the return flow of the propulsion currents may beconfined coujointly to the tracks.

Each of the track sections intermediate the insulating joints 7 and 7 ofthe tracks 3 and at respectively, constitutes a block-section of thesignaling system, each block section being provided with a signalingdevice 9 and a track transformer 10, a primary winding 11 of which isconnected to mains 12 of the signaling supply circuit, and a secondarywinding 13 of which is connected across the rails of a track section. Asthis is a usual arrangement for the signaling system. furtherexplanation thereof is not deemed necessary.

Adjacent to each other and on both sides of the insulating joints '7 and7, impedance bonds let and 14, respectively are inserted, which comprisecurrcnt-carrying windings provided with taps 15 and 15, respectively, attheir mid-points.

An intelligence transmission conductor 16, shown as a telegraph circuit,is disposed in proximity to the trolley conductors 1 and 2 and thetracks 3 and at and is, therefore, under the inductive influencesarising from the power currents flowing in the railway system. It isimportant, therefore, to minimize the inductive disturbances that may beimpressed upon the conductor 16 in order to insure satisfactoryoperation of the tele graph circuit. At the same time, the tracks areinterconnected with each other in order to provide a return conductor oflow impedance for the propulsion currents. In addition, it is to beunderstood that the signaling devices 9 must operate independently ofone another in order to amply protect the railway trafiic accommodatedupon the railway system. To this end, transformers 17 and 18 areprovided, each of which comprises a plurality of windings that areconnected to the railway circuits, as will be here inafter described.

Since the railway circuit comprising the trolley conductor 1 and thetrack is similar in all respects to the other railway circuit, mydescription will be confined to the operation of the former.

Referring particularly to a block section 19 formed in the track 3, itwill be noted that the insulating joints 8 are inserted substantiallymidway in the block section. Since the signaling currents for operatingthe signaling device 9 mustbe shunted across the 1nsulating joints 8,mutually inductivelyrelated windings 20 and 21 are connected :besubstantially unimpeded. A winding 26,

wound on the same core member as the windings 20 and 21, is connectedacross the insulating joint inserted in the trolley conductor 1, andasecond winding 26 is a connected to the trolley conductor 2 in shuntrated with the track 4, and vice versa.

to the insulating joint 6 which corresponds to the insulating joint 5 ofthe trolleyconductor ,1. A secondary winding 27 is connected, in a usualmanner, through impedance bonds 14: to the track 4. The windings 26 and27 constitute primary and secondary windings, respectively, of a seriestransformer that inductively interlinks the trolley conductor 2 with thetrack 4. y This series transformer may be considered as being embodiedin the transformer 18 which, for convenience, comprises a single coremember (not shown) having the windings --21, 26-26 and 27 woundthereuponin proper relationship, as hereinbefore explained.

Reference may now be had to the transformer 17 whichresembles thetransformer 18 in all-respects, with the exception that thosetransformer windings of the transformer 18 which are associated with thetrack 3 are, in the transformers 17, associ I For instance, windings 20and 21 are connected across the insulating joints 8 of the track 4., thewinding 20 being provided with a tap 22 disposed at its mid-point andconnected through a conductor 23 to one ter minal of an impedance coilThe winding 21 is similarly provided with a tap 22 which is connected aconductor 24 to the other terminal of the impedance coil 25. A primarywinding 26 is connected in shunt to the insulating joint 5 of thetrolley conductor 1, and a secondarywinding 27* is connected to themid-points of impedance bonds 14' which are disposed 011 both sidesof'the insulating joints 7 in the track 3. Another winding 26corresponding to the winding 26 of the transformer 18, is connected inshunt to the insulating joints 6 of thetrolley conductor 2. From theforegoing description, it will be noted that the trolley conductors 1and 2 are inductively interlinked at alternate points with the track 3and with the track 4.

It will be understood that, when the return propulsion currents areallowed to flow through the ground, a very large inductive loop isthereby formed and that the inductive interference with any nearbyintelligence-transmission conductor therefore tends to become excessive.By dividing the propulsion currents, in the manner hereinafter to bedescribed, among the various tracks of the railway system, I, am able tomaterially reduce the size of the inductive loop formed and subsequentlydecrease the amount of inductive interference.

As-mentioned above, the two tracks 3 and 4- areelectricallyinterconnected to pro vide a return conductor of low impedance for thepropulsion currents, and this is effected through the impedance coils 25and 25. To illustrate: The winding of the impedance coil 25 is providedwith a tap 28 at its mid'point which, in turn, is connected by aconductor 29 to a mid-point tap on the winding 27, the latter beingconnected throughithe impedance bonds 14k and 14 to the track 4;.Similarly, the winding of the impedance bond 25 is provided with a tap28* at its mid-point which is connected, by

a conductor 29, to a mid-point tap 30 of the winding 27, the latterbeing connected through impedance bonds 14: to the track 3. Assume thatalternating propulsion current is traversing the track 3. By reason ofthe discontinuity of the rails of track 3, be-

causeof the insertion of the insulating joints 8, a portion of thiscurrent will traverse the entire length of windings 20 and 21 and theother portion will traverse simulta-neously portions only of thewindings 20 and 21 in its endeavor to bridge the insulating joints 8.The mid-points of the windings 20 and '21, as explained above, areconnected to the terminals of the impedance coil 25, the mid-point 28 ofwhich is connected, through the conductor 29, to the mid-point 30 of thewinding 27.

By reason ofthe relatively high impedance offered by the windings 20 and21 to the flow therethrough of alternating currents traversing the tworails of the track 3 in the same direction, a portion of these currentswill take the path afforded by the conductors 23 and 24, extendingrespectively from the mid-points of the windings 20 and 21, the winding25, which offers substan tially zero impedance, and the conductor 29 tothe mid-point 30 of the winding 27.

The terminals of the winding 27 are connected to mid-points 15 and 15 ofthe impedance bonds 14 and 1 1 that are connected across the rails ofthe track 1. By introducing propulsion currents from the track 3, asexplained above, through the conductor 29, the mid-point 30 of thewinding 27 and either the mid-points 15 or 15 of the impedance bonds 14and i i, respectively, the currents are permitted to flow to the trackel, which is desired, since the two tracks 8 and 4 are thus electricallyconnected to each other to furnish conjointly a return path of lowimpedance for the propulsion currents. The impedance coils 25 and 25,therefore, furnish means for interconnecting the mutually inductivelyrelated windings Q0 and 21 of the track 3 and the mutually inductivelyrelated windings 20 and 21 of the track 4 to the secondary windings 2?and 27 respective y, of the tracks 3 and i. As a consequence, the tracks3 and i are electrically connected to each other, as regards thepropulsion currents, but the separate block-sections of the tracks aremaintained electrically independent of one another, as regards thesignaling currents.

Assuming that the block section 19 is open to traiiic, the signalingdevice 9 indicates an open block since the signaling currents traversefreely the mutually inductively related windings 20 and 21 of thetransformer 18 by being oli'ered negligible impedance only. Thesignaling currents flowing simultaneously and in opposite directionsthrough the said windings neutralize the inductive effects that wouldnecessarily be occasioned by a uni-directional current flowtherethrough. The impedance coil 25, while connectel. across thewindings 20 and 21, precludes the flow therethrough of the signalingcurrents, inasmuch as it acts in the same manner as the impedance bonds14. The signaling currents, therefore are forced to flow through theassociated relay of the signaling device 9. l'ZVhen a railway train,such as indicated at 31, bridges the block section 19, the signalingcurrents are shunted through the trucks oi the train, therebyshort-circuiting the signaling device 9 which operates to indicate thata train occupies the block 19. it will be noted that the impedance boncs i l" cenfine the signaling currents to the insulated blocir section19, thereby pemitting each block section to be operated independently ofthe others The propulsion currents supplied to the train 31 willtraverse the primary winding 26* of the transformer 17', and the primarywinding 26 or" the transformer 18, wiich windings are connected acrossthe insulating joints 5 inserted in the trolley corductor 1. The flow ofthe trolley currents through the primary windings of the trans formersl7 and 18 will induce compensating electromotive "forces-in thesecondary windings whereby the return flow of the propulsion currentsmay be confined to the tracks 3 and 4. The secondary winding 2'?directly connected to the track 3 through the impedance bonds 14- {LHChconsequently, the return flow of a portion of the propulsion currentsmay be directed theretlnough in the 1 graph circuit 16.

usual manner. The propulsion currents flowing from the train ill willreturn through each of the rails ot the block section 19 and through atleast a portion ol? the windings 20 and Eli which, as before mentioned,are connected across the insulating joints 8. Under the particularconditions assumed, substantially one-half of the propulsion currentsmay ilow through the whole of the windings 20 and El and return through.the track 2. The other hall of the propulsion currents may flowsimultaneously from the taps 2 and 522 along the conductors Q3 and 24:and oppositely thrmrgh the winding of the in'ipedance coil 25 lo themid-point tap 28. From the tap 28 they may iiow through the conductor 29to the tap of the secondary winding 27 and then traverse one-halt oi thesecondary winding 2'? to the impedance bond i l by means of which theyare directed into the rails ot the track 4. The portion of thepl'Ol'llllsion current flowing through the impedance coils 25 and 25will be oll'erod negligible impedance since the induction resulting fromthe oppositely-directed current flow therethrough is substantiallyneutralized. It will be noted that the t'ans'liormers 1'? and is providemeans itCl interchanging the current flow in the tracks 3 and 41-,inasmuch as the transformers l7 and 18 are similar, in all respects, thecorresponding windings thereof, however being connected to the dillcreut railway circuits, as liQI'OllllIlQfOlO explained It may bedesimhlc, under certain operating conditions, to design the severalcircuits so as to have a uniform impedance pe' unit length of track. Inthis manner the return how of the propulsion currents will hesuhstal'itially equally divided between the tracks and a which resultsin providing a return conductor 05 very low impedance. This apparent byconsidering that the trolley or primary currentsupplicd to the train 31will flow through the primary winding 9.6 of the transformer 18,necessiorting that a portion of the return current llow through thecoils 20 and 21. (hie-hall" ol the return current will. in thisinstance, return through the track 3, and the other hal t of thepropulsion current will llow through portions only of the coils Q0 and21 to the mid-point taps 22 and 22 by means of which it is conducted tothe track From the foregoing description, it will he observed that thereturn flow ol the propulsion current is confined to the tracks, therebyminimizing the inductive disturbances that may be impressed upon thetelei\ t the same time. each block .l'eii lOll is electricallycontinuous to the signaling currents and provides a path ol low impedan.:e therefor. Moreover, the tracks 3 and -l are electricallyintercmmectml in order that tl'iepropulsion currents may arranged instaggered relationship in the tracks, and insulating joints inserted atcorresponding points in both tracks, of means for-inductivelyinterlinking each trolley conductor to its associated track, mutuallyinductivelyrelated windings for bridging the insulating jointspositioned at intermediate points in the block-sections, andequal iningmeans for equalizing the return flow of the propulsion currentsin thetwotracks,

said equalizing means comprising inductively related coils: connected"between said tracks and, in turn, inductively interlinked with saidmeans whichwserve to interlink said trolley conductor and said track;

In an electric railway system, the combination with two tracks eachhaving an associated trolley conductor and comprising a plurality ofinsulated block sect1ons, and insulatin joints which are arranged instag:

gered re ationship with respect to one an other in thetracks inserted inthe rails intermediatethe ends ofthe block sections,of current-carryingwindings connected in shunt to said insulating joints and being mutuallyinductivelyfrelated to one another, and impedance coils havingtheirterminals connected to the mid-pointsof said currentcarryingwindings of one track and their midpoints connected to the other track.i

3. In an electric railway system, the combination with two tracks eachhaving an associated trolley conductonsaid tracks comprisinginsulatedblock sections whichare arrangedin staggered relationship in the tracksa and insulating joints inserted at correspondingpoints in both tracks,of trans formers located at the insulating joints in a the tracks, saidtransformers COIDPI'lSIIl w ndings for inductively interlinkingbottrolleyconductors alternately to said tracks,

a and mutually inductively related windings for bridging the insulatingjoints positioned inthe rails intermediate the ends of the a blocksections, and impedance coils having theirterininals connectedto themid-points of alternate groups of said mutually inductively relatedwindings and their mid-points connected alternately to the mid-points ofthe aforementioned windings associated with the tracks wherebythe returnflow of the propulsioncurrents in the tracks may beequal 4:. In anelectric railway system, the combination with two tracks each having anassociated trolley conductor, said tracks comprising blocksections whichare arranged in staggered relationship with respect to one another inthe tracks, and insulating joints in serted at corresponding points inboth tracks and both trolley conductors, of transformers for inductivelyinterlinking the trolleys and tracks to one another comprising means forbridging the insulating joints at intermediate points in theblock-sections, and equalizing means for equalizing the return flow oftransformers located at the insulating joints for inductivelyinterlinking both trolley conductors with the tracks, said transformerscomprising mutually inductively related windings for bridging theinsulating joints intermediate the ends of the blocksections, andequalizing means for electrically interconnecting said tracks to eachother whereby the return flow of the propulsion currents may be dividedbetween both tracks, said equalizing means comprising inductivelyrelated coils connected between said tracks and, in turn, inductivelyinterlinked withsaid means which serve to interlink said trolleyconductor and said track.

6. In an electric railway system, the combination with two tracksez-ichhaving an associated trolley conductor, spaced insulating jointsinsertedat corresponding points in the tracks and the trolleyconductors,"and impedance bonds connected to each track on both sides ofalternate insulating joints and staggered in position with respect toone another in the two tracks, of transformers for inductivelyinterlinking the tracks andtrolley conductors with one another, eachoffsaid transformers comprisinga common core member, primary windingsconnected in shunt to the insulating joints inserted in the trolleyconductors, a secondary winding which is connected through saidimpedance bonds to one track and mutually inductively related windingswhich are connected across insulating joints in the other track, andimpedance coils havingtheir terminals connected to mid-points ofsaidmutually inductively related windings and their mid points connected tomid-points of saidsecondarywindings. s a

. and also as the two sides of the signaling current circuits, thecombination of a pair of tracks, eachcomprising a pair of rails, aninsulating joint in each of said rails, a transformer having threewindings, each of said windings havin a midtan two of said g; 1

windings being connected respectively across the insulating joints ofthe rails of'one of said. tracks, an induction device connected betweenthe mid-taps of said two windings, said inductance device havinga mid-tap connected to the mid-tap of the third winding of said transformer, anda pairo'f additional inductance devices, one of said additionalinductance devices connecting the rails of the other of said tracks oneach side of said insulating joints, said additional inductance deviceshaving mid-taps connected respectively to the ends of said thirdtransformer winding.

8. A system as specified in clainr'l', includingtwo additional windingson the transformer, a trolley conductor for each track, and aninsulatingjoint in each of said trolley conductors, said additionaltransformer windings being connected across the insulating joints of therespective trolley conductors.

7 one of said tracks oneach side of said insulating joints, whereby thesignaling currents onopposite sides of said insulating joints arerendered independent of each other, each of said inductance deviceshaving a mid-tap, an additional inductance device connecting saidmid-taps, said additional inductance device also having a midtap,bridging means for bridging the insulating joints of the other track,and means associated with the last-mentioned mid-tap and said bridgingmeans for equalizing the propulsion currents flowing across saidinsulating joints'in the same direction in all of said rails.

10; A system as specified in claim 9, including a trolley-conductor foreach track, an insulating joint in each of said trolley conductors, andmeans bridging said trolley conductor joints for confining the flow ofreturn-current to said rails.

11. In an alternating-current railway signaling system of thetypewherein the two rails of each track serve as parallel paths for thereturn flow of propulsion currents and also as to the two sides of thesignaling current circuits, the combination of a pair of tracks, eachcomprising a pair of rails, an insulating joint in each of said rails,and means comprising windings bridging the insulating joints in therespective tracks for forming a continuous path for propulsion currentsand inductively related windings associated with the two tracks wherebythe return flow of propulsion currents across said insulating joints isequalized in all four rails, and whereby the signaling currents in thetwo tracks are kept independent of one another.

12. A system as specified in claim 1.1, including a trolley conductorfor each track, an insulating joint in each of said trolley conductors,and means bridging said trolley-conductor joints for confining the flowof return-current to said rails.

13; In an alternating-current railway signalingsystem of the typewherein the two rails of each track serve as parallel, paths for thereturn flow of propulsion currents and also as the two sides of thesignaling current circuits, the combination of a pair of: tracks, eachcomprising a pair of rails, an insulating joint in each of said rails, apair of inductively related windings bridging' the insulating joints ofthe respective rails of one of said tracks, each of said windings havinga mid-tap, bridging means bridging the insulating joints of the othertrack, and means associated with said mid-taps and with said bridgingmeans for equalizing the propulsion currents flowing across saidinsulating joints in the same direction in all of said rails.

14:. A system as specified in claim ltl. incl uding a trolley conductorfor each track. an insulating joint in each of said trolley conductors,and means bridging said trolleyconductor joints for confining the flowof re turncurrent to said rails.

15. In an electrical transmission system. the combination, of two pairsof conductors adapted for the sinniltancous transmission of two separatecomponent alternating urrents, the two conductors of each pair scriallyconstituting the circuit of one of said component currents and inparallel one side of the circuit of the other of said componentcurrents, an insulating joint inserted in ouch of said conductors. a;transformer having three windings, each of said windings ha ving amid-tap, two of saidwindings being connected respectively across theinsulating joints of the conductors of one of aid. pairs, an inductancedevice connected between the mid-taps of said two windings, saidinductive device having a mid-tap connected. to the mid-tap of the thirdwinding of said transformer, and a pair of additional inductancedevices, one of said additional inllll ductance devices connecting theconductors of the other of said pairs on each side of said insulatingjoints, said additional in ducta-nce devices havingmid-taps connectedtional transformer windings being coni so nectedgacross the insulatingjoints of the res eetive third conductors.

1 In an electrical transmission system, the combination of two pairs ofconductors adapted for the simultaneous transmission sorted in each ofsaid conductors, an in duetance devlce'eonnectmg the conductors of oneof said pairs on each side of the insulating joints, whereby the firstmentioned component currents onopposite sides of said insulating jointsare rendered independent of each other, each of said inductance deviceshaving a mid-tap, an additional inductance device connecting, saidmid-taps,

said additional inductance device also having a mid-tap, bridging meansfor bridging the insulating joints of the other pair of I conductors,and means associated with the last mentioned mid-tap and. said bridgingmeans for equalizing the second mentioned component currents flowingacross said insulating joints in the same direction in all j, of saidconductors.

18. A system as specified in claim 17, in-

eluding a third conductor for each pair, an

insulating joint in each of said third condnctors, and meansbridgingsaid third conductor joints, whereby the sum of the currents insaid third conductors and the sum of the currents in said pairs ofconductors 1 may be substantially equalized.

component currents and in arallel one side of the circuit of the other 0said component currents, an insulating joint inserted in each of saidconductors, and means comprising windings bridging the insulating jolntsin the respective pairs for forming a continuous path for the secondmentioned component currents and inductively related windings associatedwith the two pairs of conductors whereby the flow of said secondcomponent currents across said insulating joints is equalized in allfour conductors, and whereby the first mentioned component currents inthe two pairs of conductors are kept independent of one another.

20. A system as specified in claim 19, ineluding a third conductor foreach pair of conductors, an insulating joint in each of said thirdconductors, and means bridging said third conductor joints, whereby thesum of the currents in said third conductors and the sum of the currentsin said pairs of conductors may be substantially equalized.

21. In an electrical transmission system, the combination of two pairsof conductors adapted for the simultaneous transmission of two separatecomponent alternating currents, the two conductors of each pair seriallyconstituting the circuit of one of said component currents and inparallel one side of the circuit of the other of said componentcurrents, an insulating joint inserted in each of said conductors, apair of inductively related windin s brid in the insulatinfl C C) if) Cjoints of the respective conductors of one of said pairs, each of saidwindings having a a mid-tap, bridging means bridging the insulatingjoints of the other pa r, and means associated with said mid-taps andwith said bridging means for equalizing the second mentioned componentcurrents flowing across said insulating joints in the same direction inall of said conductors.

22. A system as specified in claim 21, in-

cluding a third conductor for each pair of conductors, an insulatingjoint in each of said third conductors, and means bridging said thirdconductor joints, whereby the sum of the currents in said thirdconductors and the sum of the currents in said pairs of conductors maybe substantially equalized.

In testimony whereof, I have hereunto subscribed my name this 22nd dayof Dec.

CHARLES r. soorr.

